McGinnity was in line to play his first game of AFL football against the Bombers at Subiaco Oval after some good form with WAFL club Claremont but his season is now over.
He was drafted out of the colts last year, but has played 11 league games in 2008 under Roger Kerr and averaged 17 possessions, including 34 in the Tigers' win over South Fremantle in round 15.
Eagles’ assistant coach Darren Harris said on Friday that McGinnity faced six to eight weeks on the sidelines.
"It has caught us a bit by surprise today and it's disappointing for him because he had been going really well at Claremont. Someone else could come into the 25 now, if we have anyone available," Harris said.
With Brent Staker and Josh Kennedy this week joining an ever-growing list of players with season-ending surgery, the Eagles have less and less players to pick from.
But Harris still believed there was pressure on players to perform.
"We are still trying to pick our best available 22 every week. There hasn’t been as much debate as there usually is when you have a full squad to pick from, though," he said.
"There is still pressure on us to perform every week. They are on the big stage of playing football in front of home crowds and they still want to be playing well and doing everything they can to help us win."
As for Essendon, Harris is looking forward to seeing how they handle the expanses of Subiaco Oval and to see the battle between ruckmen Dean Cox and David Hille.
"It will be interesting to see how they handle the longer ground with their running. Our game against St Kilda here was very good, we were very competitive last week apart from a 15-minute patch in the first quarter and if we can give our fans something to cheer about early we will be a big show," he said.
"David Hille always seems to grow a leg against us so it will be a massive challenge to Coxy. Hille runs offensively very well but is also very good at stoppages. He has a lot of clearances and Coxy is going to have to pick his right time to run forward and defend."
